Loans - Summary of Loan Balances (Detail) - USD ($) $ in Thousands	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Loans and Leases Receivable Disclosure [Line Items]
Total principal balance of loans owed, net of charge-offs	$ 4,351,725	$ 4,075,244
Unamortized net deferred loan fees	(8,927)	(9,868)
Discounts to principal balance of loans owed, net of charge-offs	(35,432)	(43,362)
Total	4,307,366	4,022,014	$ 3,015,165
Allowance for loan losses	(30,616)	(32,582)	(30,323)	$ (32,503)
Mortgage Loans on Real Estate
Loans and Leases Receivable Disclosure [Line Items]
Total	3,328,290	3,143,100	2,300,322
Allowance for loan losses	(14,301)	(15,620)	(13,758)	(14,265)
Consumer
Loans and Leases Receivable Disclosure [Line Items]
Total	445,542	418,982	356,874
Allowance for loan losses	(7,778)	(8,375)	(8,227)	(10,310)
Commercial
Loans and Leases Receivable Disclosure [Line Items]
Total	283,707	276,548	220,412
Allowance for loan losses	(5,149)	(6,090)	(6,512)	(5,831)
Construction
Loans and Leases Receivable Disclosure [Line Items]
Total	249,827	183,384	137,557
Allowance for loan losses	(3,388)	(2,497)	(1,826)	(2,097)
Residential 1-4 family | Mortgage Loans on Real Estate
Loans and Leases Receivable Disclosure [Line Items]
Total	509,508	515,262	385,426
Allowance for loan losses	(2,306)	(2,676)	(2,317)	(2,748)
Home equity loans | Consumer
Loans and Leases Receivable Disclosure [Line Items]
Total	28,586	36,684	43,031
Allowance for loan losses	(611)	(1,540)	(1,841)	(2,644)
Other | Consumer
Loans and Leases Receivable Disclosure [Line Items]
Total	82,656	55,721	25,155
Allowance for loan losses	(1,595)	(793)	(586)	(622)
Commercial
Loans and Leases Receivable Disclosure [Line Items]
Allowance for loan losses		(663)
Commercial | Mortgage Loans on Real Estate
Loans and Leases Receivable Disclosure [Line Items]
Total	2,818,782	2,627,838	1,914,896
Allowance for loan losses	(11,995)	(12,944)	(11,441)	(11,517)
Commercial | Construction
Loans and Leases Receivable Disclosure [Line Items]
Total	46,861	62,088	69,627
Allowance for loan losses	(318)	(663)	(642)	(680)
Home equity lines of credit | Consumer
Loans and Leases Receivable Disclosure [Line Items]
Total	334,300	326,577	288,688
Allowance for loan losses	(5,572)	(6,042)	(5,800)	(7,044)
Residential
Loans and Leases Receivable Disclosure [Line Items]
Allowance for loan losses		(1,834)
Residential | Construction
Loans and Leases Receivable Disclosure [Line Items]
Total	202,966	121,296	67,930
Allowance for loan losses	(3,070)	(1,834)	$ (1,184)	$ (1,417)
Originated
Loans and Leases Receivable Disclosure [Line Items]
Total principal balance of loans owed, net of charge-offs	3,496,622	2,991,324
Unamortized net deferred loan fees	(8,927)	(9,868)
Total	3,487,695	2,981,456
Allowance for loan losses	(30,110)	(31,793)
Originated | Mortgage Loans on Real Estate
Loans and Leases Receivable Disclosure [Line Items]
Total	2,594,318	2,254,777
Originated | Consumer
Loans and Leases Receivable Disclosure [Line Items]
Total	392,693	351,133
Originated | Commercial
Loans and Leases Receivable Disclosure [Line Items]
Total	262,581	228,635
Originated | Construction
Loans and Leases Receivable Disclosure [Line Items]
Total	238,103	146,911
Originated | Residential 1-4 family | Mortgage Loans on Real Estate
Loans and Leases Receivable Disclosure [Line Items]
Total	373,101	343,796
Originated | Home equity loans | Consumer
Loans and Leases Receivable Disclosure [Line Items]
Total	25,343	32,660
Originated | Other | Consumer
Loans and Leases Receivable Disclosure [Line Items]
Total	67,896	34,020
Originated | Commercial | Mortgage Loans on Real Estate
Loans and Leases Receivable Disclosure [Line Items]
Total	2,221,217	1,910,981
Originated | Commercial | Construction
Loans and Leases Receivable Disclosure [Line Items]
Total	46,422	56,208
Originated | Home equity lines of credit | Consumer
Loans and Leases Receivable Disclosure [Line Items]
Total	299,454	284,453
Originated | Residential | Construction
Loans and Leases Receivable Disclosure [Line Items]
Total	191,681	90,703
PNCI
Loans and Leases Receivable Disclosure [Line Items]
Total principal balance of loans owed, net of charge-offs	838,425	1,062,655
Discounts to principal balance of loans owed, net of charge-offs	(29,170)	(36,320)
Total	809,255	1,026,335
Allowance for loan losses	(500)	(667)
PNCI | Mortgage Loans on Real Estate
Loans and Leases Receivable Disclosure [Line Items]
Total	727,238	878,193
PNCI | Consumer
Loans and Leases Receivable Disclosure [Line Items]
Total	51,644	66,201
PNCI | Commercial
Loans and Leases Receivable Disclosure [Line Items]
Total	18,649	45,468
PNCI | Construction
Loans and Leases Receivable Disclosure [Line Items]
Total	11,724	36,473
PNCI | Residential 1-4 family | Mortgage Loans on Real Estate
Loans and Leases Receivable Disclosure [Line Items]
Total	134,994	169,792
PNCI | Home equity loans | Consumer
Loans and Leases Receivable Disclosure [Line Items]
Total	2,829	3,585
PNCI | Other | Consumer
Loans and Leases Receivable Disclosure [Line Items]
Total	14,758	21,659
PNCI | Commercial | Mortgage Loans on Real Estate
Loans and Leases Receivable Disclosure [Line Items]
Total	592,244	708,401
PNCI | Commercial | Construction
Loans and Leases Receivable Disclosure [Line Items]
Total	439	5,880
PNCI | Home equity lines of credit | Consumer
Loans and Leases Receivable Disclosure [Line Items]
Total	34,057	40,957
PNCI | Residential | Construction
Loans and Leases Receivable Disclosure [Line Items]
Total	11,285	30,593
PCI
Loans and Leases Receivable Disclosure [Line Items]
Total principal balance of loans owed, net of charge-offs	16,678	21,265
Discounts to principal balance of loans owed, net of charge-offs	(6,262)	(7,042)
Total	10,416	14,223
Allowance for loan losses	(6)	(122)
PCI | Mortgage Loans on Real Estate
Loans and Leases Receivable Disclosure [Line Items]
Total	6,734	10,130
PCI | Consumer
Loans and Leases Receivable Disclosure [Line Items]
Total	1,205	1,648
PCI | Commercial
Loans and Leases Receivable Disclosure [Line Items]
Total	2,477	2,445
PCI | Residential 1-4 family | Mortgage Loans on Real Estate
Loans and Leases Receivable Disclosure [Line Items]
Total	1,413	1,674
PCI | Home equity loans | Consumer
Loans and Leases Receivable Disclosure [Line Items]
Total	414	439
PCI | Other | Consumer
Loans and Leases Receivable Disclosure [Line Items]
Total	2	42
PCI | Commercial | Mortgage Loans on Real Estate
Loans and Leases Receivable Disclosure [Line Items]
Total	5,321	8,456
PCI | Home equity lines of credit | Consumer
Loans and Leases Receivable Disclosure [Line Items]
Total	$ 789	$ 1,167